Vacuum pump



g- 26, 1952 A. P. COLAIACO arm. 2,608,343

VACUUM PUMP Filed May 28, 1949 T (D N N ll" I |0- we? a I I 9 2 H llll111% 2 2' w I N N WITNESSES: INVENTORS 6 August RColoiuco and DwightL.Hopper.

BYJ ,4. $5M

ATTORNEY Patented Aug. 26, 1952 VACUUM PUMr August P. Colaiaco,Pittsburgh, Pa., and Dwight L. Hopper, Jacksonville, Ill;, assignorstoWestinghouse Electric Corporation, East Pittsburgh, Pa.,acorporationofPennsylvania sp nt-tummy 28, 1949; ea No. 95,933

Our invention relates to a vacuum pump, and

particularly to an oil diffusion pump having high pumping speeds againsthigh back pressure.

In conventional designs of vapor pumps, high speed has been obtained byhaving a first stage with a large pumping radius (the pumping radiusbeingthe. distance between the edge of the first stage jet-and theinside Wall of the pump barrel) and decreasing the pumping radius ofeach successive stage to produce a decrease of pumping radii from theintake to the exhaust end of the pump. Heretoforc, this "decrease ofpumping radii has been obtained by using a substantially uniformdiameter pump barrel and increasing the diameter of the pumping stagesfrom the first through the pumping vapor is of material quantity.Consequently, these high speed pumps will not exhaust against a highback pressure and it is accordingly customary to use a booster pump toincrease the exhaust pressure so that a secondary or mechanical vacuumpump will be eflicient in discharging the pumped gases. i

According to our invention; we have provided a diffusion pump havinghighpumping speeds and capable of exhausting against high back pressures, sothat a booster pump may be dispensed with.

In a construction according to our invention, each of the pumping jetsor stages is of substantially uniform diameter and the pump barrel issubstantially irustroconical converging from a large intake opening to arelatively small exhaust opening. By this manner, the large pumpingradii of the first stage is obtained and the small pumping radii of thelast stage is obtained, but with the additional advantage that the crosssectional area of the exhaust stage is relatively small, so that almostno back streaming results and the pump therefore will operate againstthe high back pressures normal for booster pumps.

It is possible and practical to fit a small spinning into a smallopening with much smaller tolerances than are required when fittinglarge spinnings into large openings. Consequently, in a pump accordingto our construction, the pumping radii and the exhaust area can be mademuch smaller and precise than in the heretofore conventional type pumps.

In the conventional pumps having a plurality of pumping jets fed from asingle vapor chimney, starvation of the jets farthest removed from the 1Claim. (Cl. 230-101) source of vapor has frequently been "observed.Thisstarvation results primarily from the-ex haustion of the gas by itsbeing utilized by the jets nearest the source of vapor or by coolingwhich reduces the volume of the vapor. We have found that by introducingthe'vapor fromthe pump intermediate. the jets, th vapor reaches "all ofthe jets at substantially the same pressuregthus materially increasingthe effectiveness of the pump. When it is desired to distribute thepres-f sure in some particular order the vapor inlet may be shifted tointroduce the vapor at or near the point where the highest pumpingpressure is desired. i In order toprovide a" relatively short distancefrom the boiler or other source of vapor to the pumping chimney, weprovide a horizontal pump with a boiler attached adjacentthe mid portionof the pump, so that a relatively short vapor passage connects. theboiler to an intermediate portion of the chimney. I

- It isaccordingly' an object of our invention to provide a high speed,high pressure vacuum pump.

It is a further object. of our invention to pro vide a vacuum pump inwhich the pumping area decreases Irom the intake the pump.- v f r a 1-It is a further1 object of our invention to provide a. vapor. pumphaving substantially. uniform or controlled vapor pressures to allpumpingjets.

Other objects and advantages of our invention will be apparent from thefollowing detailed description taken in conjunction With theaccompanying drawing, in hich the figure is a sectional elevation of avapor condensation pump according to our invention.

In the exemplary embodiment of our invention, a vapor diffusion pumpcomprises a substantially frustroconical body or barrel portion 10having cooling coils H applied to the exterior surface thereof so thatthe interior surface l2 of the barrel I0 is a cooling surface for thepumping vapors. Substantially axially arranged in the pumping barrel isa chimney or supply pipe IE on which is arranged a plurality of pumpingjets l6. Preferably, these jets l6 are substantially uniform indiameter, so that each of the spinnings, except the initial stage Hi,can be identical spinnings.

Usually it is preferred to provide the initial spinning it in the formof a cap I'l substantially closing the initial end of the vapor chimney15, but obviously the first stage Hi can be exactly like all of theother stages and the cap either to the exhaust end of 3 dispensed withor provided as a portion of the chimney 5. The larger intake end l8 ofthe pumpfibarrel H1 is connected to the space |9 to be evacuated and thesmaller or exhaust end 20 of the barrel H) is connected to any sort ofsecondary vacuum pump.

A boiler 2| is attached to the pump adjacent the central portion thereofand has a vapor tube 22 extending from the boiler 2| to a junction 23with the chimney l substantially adjacent the mid portion thereof or atleast intermediate the ends of the chimney I5 and. between the pumpingstages Hi.

In order to prevent cooling of the vapor between the boiler 2| and thepumping chimney I5, a plurality of concentric tubes or shields 24 and 25are placed around the vapor passage 22 and are open to the interior ofthe pump, so that a, low pressure will be maintained in the spacebetween the concentric tubes 24-25 and the vapor passage 22. Preferablythe portions of the chimney |5' are mounted on and supported by thevapor tube 22 so that different types of pumps may be constructed bysimply screwing in portions of the chimney |5 having the desired pumpingjets Hi. In order to return condensed pumping material to the boiler 2|,a return pipe 26' is provided from adjacent the large end It! of thebarrel Hi to a point adjacent the bottom of the boiler 2|. Usually somesort of barrier 27 is provided to prevent condensed pumping fluidpassing the inlet port of the return tube.

While any sort of heating device may be utilized for the boiler, weprefer to provide an electric heater 28 either immersed in the oil orattached in good thermal relation to the external portion of the boiler2|. Any suitable thermal insulation, not shown, may be applied to theboiler 2| or the exposed portion of the heat conserving concentric tubes24.

In the operation of the pump according to our invention, the large endI8 is attached to the space I9 to be evacuated and the exhaust end 20 toany suitable vacuum pump and heat is applied to the boiler 2| to producea flow of vapor into the chimney |5 and from the chimney l5 through thepumping jets IS. The pumping vapor entrains molecules of gas and causesthem to move from the intake to the exhaust end of the pump so that avery low pressure will be maintained at the intake and a higherpress'ureat the exhaust end of the device.

' of our invention and described the same to the best of our presentability, we wish it to be understood that changes and modifications canbe made therein without departing from the true spirit. of our inventionor the scope of the appended claim.

We claim as our invention:

A vapor pump comprising means for providing a tapering chamber, coolingmeans applied to said chamber to produce a condensing surface therein, avapor supply pipe of substantially uniform diameter from end to end,located substantially centrally within said chamber, said supply pipehaving an end-structure at each end, a plurality of difiusion jets ofsubstantially uniform diameter connected to said vapor supply pipe atspaced points along its length, said jets being directed to move gasfrom the large to the small end of said chamber, a boiler for producingpumping vapor, and connection-means for sup plying vapor from saidboiler to said vapor supply pipe, said connection-means being at a pointintermediate the ends of the vapor supply .pipe.

. AUGUST P. COLAIACO. DWIGHT L.'HOPPER.

REFERENCES CITED The following references are of record in the file ofthis patent:

' I UNITED STATES PATENTS Number Name Date 2,237,806 Bancroft Apr. 8,1941 2,390,814 Stallman Dec. 11, 1945 2,447,636 Colaiaco Aug. 24, 1948FOREIGN PATENTS Number, Country Date 75,901 Sweden Mar. 26, 1931

